About patches

About patches

[rkardell]

I explicit asked if the patches were ok when I sent them and I got no 
response. Now I received this “This patch is broken on so many ways:” 
with comments. Responses like this will certainly not encourage new 
members, especially since the comments and changes of the code was not 
of high quality. And it certainly discourage me!

I include a copy of my comments sent to the responsible person and 
de-register from the group.




Den 2021-12-07 kl. 09:29, skrev rkardell:
 >
 > Sorry if I created problems for linux-media by pointing to a solution 
to a problem that has been in the kernel since the introduction of USB 
EHCI. The only PC I have that works with this DVB device is from 2005.
 >
 > I first asked for comments since C/C++ is not my preferred language 
and Linux kernel is not my normal working environment, but I got no 
response. I submitted the patches to the best of my knowledge.
 >
 >
 > 1. Your documented way of submitting patches did not work, so I had 
to retrieve the patch and send it as an ordinary mail.
 >
 > 2. If you cant get 1 byte buffer in the kernel, then you wont reach 
this code, but yes I could have tested.
 >
 > 3. I didn’t change the write code, because it was not a problem.
 >
 > 4. Sorry for that
 >
 > It is obvious that its the USB transfer that is the problem since USB 
is used for the i2c transfer!
 >
 > I have no way of knowing what combination of chips/drivers are used 
and possible side effects of changes. That’s way I preferred to change 
the the code this way
 >
 > From the documentation I found, it’s not the use of pointers on the 
stack that is the problem, its the use of buffer on the stack.
 >
 >
 > About your code: you don’t have to free memory that you could not 
allocate.
 >
 > My pc is updated with my patch, so I cant test your solution.
 >
 >
 > I don’t need this type of comment after my effort to point out the 
problem that has been in the kernel for such a long time, so I will 
de-register from the group.
 >
 >
 >
 > Den 2021-12-06 kl. 16:01, skrev Mauro Carvalho Chehab:
 >> Hi,
 >>
 >> This patch is broken on so many ways:
 >>
 >> 1. your e-mailer converted spaces and tabs into UTF spaces (0xa0);
 >> 2. it is not checking if allocation failed;
 >> 3. it doesn't fix the write function, which also uses stack;
 >> 4. you need your real name on your from and SoB.
 >>
 >> Besides that, there's no issue on using the stack for I2C transfers.
 >> The issue, is actually to use stack for USB transfers.
 >>
 >> So, the right fix should be, instead, at the bridge driver, and not
 >> on tuner. It seems that Mega Sky 580 USB DVB is supportd by m920x 
driver.
 >> Right?
 >>
 >> If so, the enclosed patch should fix the issue.
 >>
 >> Please test.
 >>
 >> Regards,
 >> Mauro
 >>
 >> Em Thu, 7 Oct 2021 14:29:00 +0200
 >> rkardell <rkardell@mida.se> escreveu:
 >>
 >>> Solve problem with initialization of Mega Sky 580 USB DVB (and other
 >>> using mt352), error when reading i2c id.
 >>>
 >>>
 >>> Signed-off-by: rkl099 <rkardell@mida.se>
 >>> ---
 >>>   drivers/media/tuners/qt1010.c | 6 +++++-
 >>>   1 file changed, 5 insertions(+), 1 deletion(-)
 >>>
 >>> diff --git a/drivers/media/tuners/qt1010.c 
b/drivers/media/tuners/qt1010.c
 >>> index 3853a3d43..1bc0756f7 100644
 >>> --- a/drivers/media/tuners/qt1010.c
 >>> +++ b/drivers/media/tuners/qt1010.c
 >>> @@ -11,18 +11,22 @@
 >>>   /* read single register */
 >>>   static int qt1010_readreg(struct qt1010_priv *priv, u8 reg, u8 *val)
 >>>   {
 >>> +    u8 *b1=kmalloc(1,GFP_KERNEL);
 >>>          struct i2c_msg msg[2] = {
 >>>                  { .addr = priv->cfg->i2c_address,
 >>>                    .flags = 0, .buf = &reg, .len = 1 },
 >>>                  { .addr = priv->cfg->i2c_address,
 >>> -                 .flags = I2C_M_RD, .buf = val, .len = 1 },
 >>> +                 .flags = I2C_M_RD, .buf = b1, .len = 1 },
 >>>          };
 >>>
 >>>          if (i2c_transfer(priv->i2c, msg, 2) != 2) {
 >>>                  dev_warn(&priv->i2c->dev, "%s: i2c rd failed 
reg=%02x\n",
 >>>                                  KBUILD_MODNAME, reg);
 >>> +           kfree(b1);
 >>>                  return -EREMOTEIO;
 >>>          }
 >>> +       *val=b1[0];
 >>> +       kfree(b1);
 >>>          return 0;
 >>>   }
 >>>
 >> Thanks,
 >> Mauro
 >>
 >> [PATCH] media: m920x: don't use stack on USB reads
 >>
 >> Using stack-allocated pointers for USB message data don't work.
 >> This driver is almost OK with that, except for the I2C read
 >> logic.
 >>
 >> Fix it by using a temporary read buffer, just like on all other
 >> calls to m920x_read().
 >>
 >> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
 >>
 >> diff --git a/drivers/media/usb/dvb-usb/m920x.c 
b/drivers/media/usb/dvb-usb/m920x.c
 >> index 4bb5b82599a7..691e05833db1 100644
 >> --- a/drivers/media/usb/dvb-usb/m920x.c
 >> +++ b/drivers/media/usb/dvb-usb/m920x.c
 >> @@ -274,6 +274,13 @@ static int m920x_i2c_xfer(struct i2c_adapter 
*adap, struct i2c_msg msg[], int nu
 >>              /* Should check for ack here, if we knew how. */
 >>          }
 >>          if (msg[i].flags & I2C_M_RD) {
 >> +            char *read = kmalloc(1, GFP_KERNEL);
 >> +            if (!read) {
 >> +                ret = -ENOMEM;
 >> +                kfree(read);
 >> +                goto unlock;
 >> +            }
 >> +
 >>              for (j = 0; j < msg[i].len; j++) {
 >>                  /* Last byte of transaction?
 >>                   * Send STOP, otherwise send ACK. */
 >> @@ -281,9 +288,12 @@ static int m920x_i2c_xfer(struct i2c_adapter 
*adap, struct i2c_msg msg[], int nu
 >>
 >>                  if ((ret = m920x_read(d->udev, M9206_I2C, 0x0,
 >>                                0x20 | stop,
 >> -                              &msg[i].buf[j], 1)) != 0)
 >> +                              read, 1)) != 0)
 >>                      goto unlock;
 >> +                msg[i].buf[j] = read[0];
 >>              }
 >> +
 >> +            kfree(read);
 >>          } else {
 >>              for (j = 0; j < msg[i].len; j++) {
 >>                  /* Last byte of transaction? Then send STOP. */
 >>
 >