Re: [PATCH v2] drivers: input: Use single i2c_transfer transaction when using RM_CMD_BANK_SWITCH

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Sun, Sep 13, 2020 at 11:04:48PM -0700, Furquan Shaikh wrote:
> Hi Dmitry,
> 
> On Tue, Sep 8, 2020 at 5:44 PM Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> >
> > Hi Furquan,
> >
> > On Thu, Aug 20, 2020 at 07:40:06PM -0700, Furquan Shaikh wrote:
> > > On an AMD chromebook, where the same I2C bus is shared by both Raydium
> > > touchscreen and a trackpad device, it is observed that interleaving of
> > > I2C messages when `raydium_i2c_read_message()` is called leads to the
> > > Raydium touch IC reporting incorrect information. This is the sequence
> > > that was observed to result in the above issue:
> > >
> > > * I2C write to Raydium device for RM_CMD_BANK_SWITCH
> > > * I2C write to trackpad device
> > > * I2C read from trackpad device
> > > * I2C write to Raydium device for setting address
> > > * I2C read from Raydium device >>>> This provides incorrect
> > >   information
> > >
> > > This change adds a new helper function `raydium_i2c_xfer()` that
> > > performs I2C transactions to the Raydium device. It uses the register
> > > address to decide if RM_CMD_BANK_SWITCH header needs to be sent to the
> > > device (i.e. if register address is greater than 255, then bank switch
> > > header is sent before the rest of the transaction). Additionally, it
> > > ensures that all the I2C operations performed as part of
> > > `raydium_i2c_xfer()` are done as a single i2c_transfer. This
> > > guarantees that no other transactions are initiated to any other
> > > device on the same bus in between. Additionally,
> > > `raydium_i2c_{send|read}*` functions are refactored to use this new
> > > helper function.
> > >
> > > Verified with the patch across multiple reboots (>100) that the
> > > information reported by the Raydium  touchscreen device during probe
> > > is correct.
> > >
> > > Signed-off-by: Furquan Shaikh <furquan@google.com>
> > >
> > > ---
> > > v2: Added a new helper function raydium_i2c_xfer so that all read and
> > > send transfers are handled using the same path. This helper function
> > > uses register address > 255 to decide whether to send
> > > RM_CMD_BANK_SWITCH command. Additionally, __packed keyword is moved
> > > to be placed after the structure defintion.
> > >
> > >  drivers/input/touchscreen/raydium_i2c_ts.c | 132 +++++++++------------
> > >  1 file changed, 58 insertions(+), 74 deletions(-)
> > >
> > > diff --git a/drivers/input/touchscreen/raydium_i2c_ts.c b/drivers/input/touchscreen/raydium_i2c_ts.c
> > > index fe245439adee..261e4a290836 100644
> > > --- a/drivers/input/touchscreen/raydium_i2c_ts.c
> > > +++ b/drivers/input/touchscreen/raydium_i2c_ts.c
> > > @@ -51,6 +51,7 @@
> > >
> > >  /* Touch relative info */
> > >  #define RM_MAX_RETRIES               3
> > > +#define RM_RETRY_DELAY_MS    20
> > >  #define RM_MAX_TOUCH_NUM     10
> > >  #define RM_BOOT_DELAY_MS     100
> > >
> > > @@ -136,114 +137,98 @@ struct raydium_data {
> > >       bool wake_irq_enabled;
> > >  };
> > >
> > > -static int raydium_i2c_send(struct i2c_client *client,
> > > -                         u8 addr, const void *data, size_t len)
> > > +static int raydium_i2c_xfer(struct i2c_client *client, u32 addr, void *data,
> > > +                             size_t len, bool is_read)
> > >  {
> > > -     u8 *buf;
> > > -     int tries = 0;
> > > -     int ret;
> > > -
> > > -     buf = kmalloc(len + 1, GFP_KERNEL);
> > > -     if (!buf)
> > > -             return -ENOMEM;
> > > -
> > > -     buf[0] = addr;
> > > -     memcpy(buf + 1, data, len);
> > > -
> > > -     do {
> > > -             ret = i2c_master_send(client, buf, len + 1);
> > > -             if (likely(ret == len + 1))
> > > -                     break;
> > > -
> > > -             msleep(20);
> > > -     } while (++tries < RM_MAX_RETRIES);
> > > -
> > > -     kfree(buf);
> > > -
> > > -     if (unlikely(ret != len + 1)) {
> > > -             if (ret >= 0)
> > > -                     ret = -EIO;
> > > -             dev_err(&client->dev, "%s failed: %d\n", __func__, ret);
> > > -             return ret;
> > > -     }
> > > +     struct raydium_bank_switch_header {
> > > +             u8 cmd;
> > > +             __be32 be_addr;
> > > +     } __packed header = {
> > > +             .cmd = RM_CMD_BANK_SWITCH,
> > > +             .be_addr = cpu_to_be32(addr),
> > > +     };
> > >
> > > -     return 0;
> > > -}
> > > +     u8 reg_addr = addr & 0xff;
> > >
> > > -static int raydium_i2c_read(struct i2c_client *client,
> > > -                         u8 addr, void *data, size_t len)
> > > -{
> > >       struct i2c_msg xfer[] = {
> > > +             {
> > > +                     .addr = client->addr,
> > > +                     .len = sizeof(header),
> > > +                     .buf = (u8 *)&header,
> > > +             },
> > >               {
> > >                       .addr = client->addr,
> > >                       .len = 1,
> > > -                     .buf = &addr,
> > > +                     .buf = &reg_addr,
> > >               },
> > >               {
> > >                       .addr = client->addr,
> > > -                     .flags = I2C_M_RD,
> > >                       .len = len,
> > >                       .buf = data,
> > > +                     .flags = is_read ? I2C_M_RD : 0,
> > >               }
> > >       };
> > > +
> > > +     /*
> > > +      * If address is greater than 255, then RM_CMD_BANK_SWITCH needs to be
> > > +      * sent first. Else, skip the header i.e. xfer[0].
> > > +      */
> > > +     int xfer_start_idx = (addr > 0xff) ? 0 : 1;
> > > +     size_t xfer_count = ARRAY_SIZE(xfer) - xfer_start_idx;
> > >       int ret;
> > >
> > > -     ret = i2c_transfer(client->adapter, xfer, ARRAY_SIZE(xfer));
> > > -     if (unlikely(ret != ARRAY_SIZE(xfer)))
> > > -             return ret < 0 ? ret : -EIO;
> > > +     ret = i2c_transfer(client->adapter, &xfer[xfer_start_idx], xfer_count);
> > > +     if (likely(ret == xfer_count))
> > > +             return 0;
> > >
> > > -     return 0;
> > > +     return -EIO;
> >
> > We are losing real error here, I'll change this to
> >
> >         return ret < 0 ? ret : -EIO;
> >
> > >  }
> 
> Looks good.
> 
> > >
> > > -static int raydium_i2c_read_message(struct i2c_client *client,
> > > -                                 u32 addr, void *data, size_t len)
> > > +static int raydium_i2c_send(struct i2c_client *client, u32 addr,
> > > +                             const void *data, size_t len)
> > >  {
> > > -     __be32 be_addr;
> > > +     int tries = 0;
> > > +     int ret;
> > > +
> > > +     do {
> > > +             ret = raydium_i2c_xfer(client, addr, (void *)data, len, false);
> > > +             if (likely(ret == 0))
> > > +                     return 0;
> > > +
> > > +             msleep(RM_RETRY_DELAY_MS);
> > > +     } while (++tries < RM_MAX_RETRIES);
> > > +
> > > +     dev_err(&client->dev, "%s failed\n", __func__);
> > > +     return -EIO;
> >
> > Again losing real error here, I'll rename ret to error and do
> >
> >         return error;
> >
> > here.
> 
> Looks good.
> 
> >
> > > +}
> > > +
> > > +static int raydium_i2c_read(struct i2c_client *client, u32 addr, void *data,
> > > +                             size_t len)
> > > +{
> > > +     int ret;
> > >       size_t xfer_len;
> > > -     int error;
> > >
> > >       while (len) {
> > >               xfer_len = min_t(size_t, len, RM_MAX_READ_SIZE);
> > > +             ret = raydium_i2c_xfer(client, addr, data, len, true);
> >
> > I think this needs to be xfer_len, not len.
> 
> Good catch. Yes, this needs to be xfer_len.
> 
> >
> > I can fix it up locally if you agree.
> 
> The suggestions look good to me. Thank you!

Great, applied.

-- 
Dmitry