| Message ID | 1534839799-14112-1-git-send-email-yamada.masahiro@socionext.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | mtd: rawnand: denali: do not pass zero maxchips to nand_scan() | expand |
Hi Masahiro, Masahiro Yamada <yamada.masahiro@socionext.com> wrote on Tue, 21 Aug 2018 17:23:19 +0900: > Commit 49aa76b16676 ("mtd: rawnand: do not execute nand_scan_ident() > if maxchips is zero") gave a new meaning for calling nand_scan_ident() > with maxchips=0. > > It is a special usage for some drivers such as docg4, but in fact > the Denali driver may pass maxchips=0 to nand_scan() when the driver > is enabled but no NAND chip is found on the board for some reasons. > > If nand_scan_with_ids() is called with maxchips=0, nand_scan_ident() > is skipped, i.e. nand_set_defaults() is skipped. Therefore, the > driver must have set chip->controller beforehand. Otherwise, > nand_attach() causes NULL pointer dereference. > > In fact, the Denali controller knows the number of connected chips > before calling nand_scan_ident(); if DEVICE_RESET fails, there is no > chip in that chip select. Then, denali_reset_banks() sets the maxchips > to the number of detected chips. If no chip is found, it is zero. > > The reason of this trick was, as commit f486287d2372 ("mtd: nand: > denali: fix bank reset function to detect the number of chips") > explained, nand_scan_ident() issued Set Features (0xEF) command > to all CS lines, some of which may not be connected with a chip. > Then, the driver would wait until R/B# response, which never happens. > > This problem was solved by commit 107b7d6a7ad4 ("mtd: rawnand: avoid > setting again the timings to mode 0 after a reset"). In the current > code, nand_setup_data_interface() is called from nand_scan_tail(), > which is after the chip detection is done. > > Remove the code that is causing NULL pointer dereference. Now, the > maxchips passed to nand_scan() is the maximum number of chip selects > supported by the IP (typically 4 or 8). Leave all the chip detection > process to nand_scan_ident(). > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Thanks for the fix. Actually the docg4 driver is getting removed and the special handling in nand_scan() about having 0 maxchips will also disappear. Nonetheless, I think the below code was buggy and I would like to apply the fix anyway. > --- > > drivers/mtd/nand/raw/denali.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c > index ca18612..3e4b8e1 100644 > --- a/drivers/mtd/nand/raw/denali.c > +++ b/drivers/mtd/nand/raw/denali.c > @@ -1086,7 +1086,6 @@ static void denali_reset_banks(struct denali_nand_info *denali) > } > > dev_dbg(denali->dev, "%d chips connected\n", i); > - denali->max_banks = i; > } > > static void denali_hw_init(struct denali_nand_info *denali) Thanks, Miquèl
Hi Masahiro, On Tue, 21 Aug 2018 17:23:19 +0900 Masahiro Yamada <yamada.masahiro@socionext.com> wrote: > Commit 49aa76b16676 ("mtd: rawnand: do not execute nand_scan_ident() > if maxchips is zero") gave a new meaning for calling nand_scan_ident() > with maxchips=0. > > It is a special usage for some drivers such as docg4, but in fact > the Denali driver may pass maxchips=0 to nand_scan() when the driver > is enabled but no NAND chip is found on the board for some reasons. > > If nand_scan_with_ids() is called with maxchips=0, nand_scan_ident() > is skipped, i.e. nand_set_defaults() is skipped. Therefore, the > driver must have set chip->controller beforehand. Otherwise, > nand_attach() causes NULL pointer dereference. > > In fact, the Denali controller knows the number of connected chips > before calling nand_scan_ident(); if DEVICE_RESET fails, there is no > chip in that chip select. Then, denali_reset_banks() sets the maxchips > to the number of detected chips. If no chip is found, it is zero. > > The reason of this trick was, as commit f486287d2372 ("mtd: nand: > denali: fix bank reset function to detect the number of chips") > explained, nand_scan_ident() issued Set Features (0xEF) command > to all CS lines, some of which may not be connected with a chip. > Then, the driver would wait until R/B# response, which never happens. > > This problem was solved by commit 107b7d6a7ad4 ("mtd: rawnand: avoid > setting again the timings to mode 0 after a reset"). In the current > code, nand_setup_data_interface() is called from nand_scan_tail(), > which is after the chip detection is done. > > Remove the code that is causing NULL pointer dereference. Now, the > maxchips passed to nand_scan() is the maximum number of chip selects > supported by the IP (typically 4 or 8). Leave all the chip detection > process to nand_scan_ident(). > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> > --- > > drivers/mtd/nand/raw/denali.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c > index ca18612..3e4b8e1 100644 > --- a/drivers/mtd/nand/raw/denali.c > +++ b/drivers/mtd/nand/raw/denali.c > @@ -1086,7 +1086,6 @@ static void denali_reset_banks(struct denali_nand_info *denali) > } > > dev_dbg(denali->dev, "%d chips connected\n", i); > - denali->max_banks = i; Shouldn't we instead avoid calling nand_scan() when denali->max_banks=0? I mean, what's the point of calling this function if you know for sure it will fail. Last question: do we still need this denali_reset_banks()? If it's only about resetting the chip to detect how many are actually present, that's already done by nand_scan(). > } > > static void denali_hw_init(struct denali_nand_info *denali)
Hi Boris, 2018-08-24 21:55 GMT+09:00 Boris Brezillon <boris.brezillon@bootlin.com>: > Hi Masahiro, > > On Tue, 21 Aug 2018 17:23:19 +0900 > Masahiro Yamada <yamada.masahiro@socionext.com> wrote: > >> Commit 49aa76b16676 ("mtd: rawnand: do not execute nand_scan_ident() >> if maxchips is zero") gave a new meaning for calling nand_scan_ident() >> with maxchips=0. >> >> It is a special usage for some drivers such as docg4, but in fact >> the Denali driver may pass maxchips=0 to nand_scan() when the driver >> is enabled but no NAND chip is found on the board for some reasons. >> >> If nand_scan_with_ids() is called with maxchips=0, nand_scan_ident() >> is skipped, i.e. nand_set_defaults() is skipped. Therefore, the >> driver must have set chip->controller beforehand. Otherwise, >> nand_attach() causes NULL pointer dereference. >> >> In fact, the Denali controller knows the number of connected chips >> before calling nand_scan_ident(); if DEVICE_RESET fails, there is no >> chip in that chip select. Then, denali_reset_banks() sets the maxchips >> to the number of detected chips. If no chip is found, it is zero. >> >> The reason of this trick was, as commit f486287d2372 ("mtd: nand: >> denali: fix bank reset function to detect the number of chips") >> explained, nand_scan_ident() issued Set Features (0xEF) command >> to all CS lines, some of which may not be connected with a chip. >> Then, the driver would wait until R/B# response, which never happens. >> >> This problem was solved by commit 107b7d6a7ad4 ("mtd: rawnand: avoid >> setting again the timings to mode 0 after a reset"). In the current >> code, nand_setup_data_interface() is called from nand_scan_tail(), >> which is after the chip detection is done. >> >> Remove the code that is causing NULL pointer dereference. Now, the >> maxchips passed to nand_scan() is the maximum number of chip selects >> supported by the IP (typically 4 or 8). Leave all the chip detection >> process to nand_scan_ident(). >> >> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> >> --- >> >> drivers/mtd/nand/raw/denali.c | 1 - >> 1 file changed, 1 deletion(-) >> >> diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c >> index ca18612..3e4b8e1 100644 >> --- a/drivers/mtd/nand/raw/denali.c >> +++ b/drivers/mtd/nand/raw/denali.c >> @@ -1086,7 +1086,6 @@ static void denali_reset_banks(struct denali_nand_info *denali) >> } >> >> dev_dbg(denali->dev, "%d chips connected\n", i); >> - denali->max_banks = i; > > Shouldn't we instead avoid calling nand_scan() when > denali->max_banks=0? I mean, what's the point of calling this function > if you know for sure it will fail. Right. If no chip is found, it should error out with -ENODEV or something. > Last question: do we still need this denali_reset_banks()? If it's only > about resetting the chip to detect how many are actually present, > that's already done by nand_scan(). I thought this too. Please give me time to answer this question. I need to check the datasheet and test on my boards. If I can remove denali_reset_banks() entirely, it would be the best. Thanks. >> } >> >> static void denali_hw_init(struct denali_nand_info *denali) >
On Sat, 25 Aug 2018 00:04:43 +0900 Masahiro Yamada <yamada.masahiro@socionext.com> wrote: > Hi Boris, > > 2018-08-24 21:55 GMT+09:00 Boris Brezillon <boris.brezillon@bootlin.com>: > > Hi Masahiro, > > > > On Tue, 21 Aug 2018 17:23:19 +0900 > > Masahiro Yamada <yamada.masahiro@socionext.com> wrote: > > > >> Commit 49aa76b16676 ("mtd: rawnand: do not execute nand_scan_ident() > >> if maxchips is zero") gave a new meaning for calling nand_scan_ident() > >> with maxchips=0. > >> > >> It is a special usage for some drivers such as docg4, but in fact > >> the Denali driver may pass maxchips=0 to nand_scan() when the driver > >> is enabled but no NAND chip is found on the board for some reasons. > >> > >> If nand_scan_with_ids() is called with maxchips=0, nand_scan_ident() > >> is skipped, i.e. nand_set_defaults() is skipped. Therefore, the > >> driver must have set chip->controller beforehand. Otherwise, > >> nand_attach() causes NULL pointer dereference. > >> > >> In fact, the Denali controller knows the number of connected chips > >> before calling nand_scan_ident(); if DEVICE_RESET fails, there is no > >> chip in that chip select. Then, denali_reset_banks() sets the maxchips > >> to the number of detected chips. If no chip is found, it is zero. > >> > >> The reason of this trick was, as commit f486287d2372 ("mtd: nand: > >> denali: fix bank reset function to detect the number of chips") > >> explained, nand_scan_ident() issued Set Features (0xEF) command > >> to all CS lines, some of which may not be connected with a chip. > >> Then, the driver would wait until R/B# response, which never happens. > >> > >> This problem was solved by commit 107b7d6a7ad4 ("mtd: rawnand: avoid > >> setting again the timings to mode 0 after a reset"). In the current > >> code, nand_setup_data_interface() is called from nand_scan_tail(), > >> which is after the chip detection is done. > >> > >> Remove the code that is causing NULL pointer dereference. Now, the > >> maxchips passed to nand_scan() is the maximum number of chip selects > >> supported by the IP (typically 4 or 8). Leave all the chip detection > >> process to nand_scan_ident(). > >> > >> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> > >> --- > >> > >> drivers/mtd/nand/raw/denali.c | 1 - > >> 1 file changed, 1 deletion(-) > >> > >> diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c > >> index ca18612..3e4b8e1 100644 > >> --- a/drivers/mtd/nand/raw/denali.c > >> +++ b/drivers/mtd/nand/raw/denali.c > >> @@ -1086,7 +1086,6 @@ static void denali_reset_banks(struct denali_nand_info *denali) > >> } > >> > >> dev_dbg(denali->dev, "%d chips connected\n", i); > >> - denali->max_banks = i; > > > > Shouldn't we instead avoid calling nand_scan() when > > denali->max_banks=0? I mean, what's the point of calling this function > > if you know for sure it will fail. > > > Right. If no chip is found, it should error out with -ENODEV or something. > > > > > Last question: do we still need this denali_reset_banks()? If it's only > > about resetting the chip to detect how many are actually present, > > that's already done by nand_scan(). > > I thought this too. > > Please give me time to answer this question. > I need to check the datasheet and test on my boards. > > If I can remove denali_reset_banks() entirely, > it would be the best. I'd like the fix to be as simple as possible, so that I can queue it for -rc2. Please consider the solution where nand_scan() is skipped when denali->max_banks=0 first. We can then decide to remove denali_reset_banks() if that's appropriate. Thanks, Boris
diff --git a/drivers/mtd/nand/raw/denali.c b/drivers/mtd/nand/raw/denali.c index ca18612..3e4b8e1 100644 --- a/drivers/mtd/nand/raw/denali.c +++ b/drivers/mtd/nand/raw/denali.c @@ -1086,7 +1086,6 @@ static void denali_reset_banks(struct denali_nand_info *denali) } dev_dbg(denali->dev, "%d chips connected\n", i); - denali->max_banks = i; } static void denali_hw_init(struct denali_nand_info *denali)
Commit 49aa76b16676 ("mtd: rawnand: do not execute nand_scan_ident() if maxchips is zero") gave a new meaning for calling nand_scan_ident() with maxchips=0. It is a special usage for some drivers such as docg4, but in fact the Denali driver may pass maxchips=0 to nand_scan() when the driver is enabled but no NAND chip is found on the board for some reasons. If nand_scan_with_ids() is called with maxchips=0, nand_scan_ident() is skipped, i.e. nand_set_defaults() is skipped. Therefore, the driver must have set chip->controller beforehand. Otherwise, nand_attach() causes NULL pointer dereference. In fact, the Denali controller knows the number of connected chips before calling nand_scan_ident(); if DEVICE_RESET fails, there is no chip in that chip select. Then, denali_reset_banks() sets the maxchips to the number of detected chips. If no chip is found, it is zero. The reason of this trick was, as commit f486287d2372 ("mtd: nand: denali: fix bank reset function to detect the number of chips") explained, nand_scan_ident() issued Set Features (0xEF) command to all CS lines, some of which may not be connected with a chip. Then, the driver would wait until R/B# response, which never happens. This problem was solved by commit 107b7d6a7ad4 ("mtd: rawnand: avoid setting again the timings to mode 0 after a reset"). In the current code, nand_setup_data_interface() is called from nand_scan_tail(), which is after the chip detection is done. Remove the code that is causing NULL pointer dereference. Now, the maxchips passed to nand_scan() is the maximum number of chip selects supported by the IP (typically 4 or 8). Leave all the chip detection process to nand_scan_ident(). Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> --- drivers/mtd/nand/raw/denali.c | 1 - 1 file changed, 1 deletion(-)