Regards
Shashank
On 8/22/2017 8:57 PM, Jani Nikula wrote:
On Tue, 22 Aug 2017, Shashank Sharma <shashank.sharma@xxxxxxxxx> wrote:
It's an observation during some CI tests that few LSPCON chips
respond slow while system is under load, and need some delay
while reading current mode status using i2c-over-aux channel.
This patch:
- Adds few retries and delays before declaring a read
failure from LSPCON hardware.
- Changes the debug level of the print from ERROR->DEBUG
whereas another patch in I915 will add an ERROR message
from the caller when we have timed out all our limits.
V2: addressed review comments from Imre, and added r-b
- use int instead of u8 for counter
- use for loop instead of do...while();
V3: Rebase
Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>
Cc: Imre Deak <imre.deak@xxxxxxxxx>
Reviewed-by: Imre Deak <imre.deak@xxxxxxxxx>
Signed-off-by: Shashank Sharma <shashank.sharma@xxxxxxxxx>
Signed-off-by: Mahesh Kumar <mahesh1.kumar@xxxxxxxxx>
---
drivers/gpu/drm/drm_dp_dual_mode_helper.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
index 80e62f6..fc8c7ac 100644
--- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
+++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
@@ -409,6 +409,7 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
enum drm_lspcon_mode *mode)
{
u8 data;
+ int retry;
int ret = 0;
if (!mode) {
@@ -417,10 +418,17 @@ int drm_lspcon_get_mode(struct i2c_adapter *adapter,
}
/* Read Status: i2c over aux */
- ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_LSPCON_CURRENT_MODE,
- &data, sizeof(data));
+ for (retry = 5; ; retry--) {
+ ret = drm_dp_dual_mode_read(adapter,
+ DP_DUAL_MODE_LSPCON_CURRENT_MODE,
+ &data, sizeof(data));
+ if (!ret || !retry)
+ break;
+ usleep_range(500, 1000);
+ }
Sorry, but that looks like a programming quiz to me. At most how many
time does drm_dp_dual_mode_read() get called?
Yes, you are correct, the loop gets called 6 times, in the initial
version of this code, I had the condition
to be if (!ret || !--retry) break; which was serving the purpose of 6
calls to drm_dp_dual_mode_read()
but only 5 delays. But later I moved some code, and messed with the logic.
I will modify this.
With this, for example, the C programmer's spine tells you "six times"
for the paradigm for loop before you even really stop to think about it:
for (try = 0; try < 6; try++) {
if (try)
usleep_range(500, 1000);
ret = drm_dp_dual_mode_read();
if (!ret)
break;
}
BR,
Jani.
PS. I'm left wondering if "retry = 5" was there to emphasize that
there's one try and five *retries*.
Actually, the aim was to do 6 call to drm_dp_dual_mode_read() but add
only 5 delays, as I wanted
the first read also in the loop. But as you rightly mention, the latest
loop was not good enough.
- Shashank
+
if (ret < 0) {
- DRM_ERROR("LSPCON read(0x80, 0x41) failed\n");
+ DRM_DEBUG_KMS("LSPCON read(0x80, 0x41) failed\n");
return -EFAULT;
}
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