On Thu, Sep 30, 2010 at 6:00 PM, Antti Palosaari <crope@xxxxxx> wrote: > On 09/30/2010 09:52 PM, Michael Krufky wrote: >> >> On Tue, Sep 28, 2010 at 2:46 PM, Mauro Carvalho Chehab >> <mchehab@xxxxxxxxxx> wrote: >>> >>> By default, tda18271 tries to optimize I2C bus by updating all registers >>> at the same time. Unfortunately, some devices doesn't support it. >>> >>> The current logic has a problem when small_i2c is equal to 8, since there >>> are some transfers using 11 + 1 bytes. >>> >>> Fix the problem by enforcing the max size at the right place, and allows >>> reducing it to max = 3 + 1. >>> >>> Signed-off-by: Mauro Carvalho Chehab<mchehab@xxxxxxxxxx> >> >> This looks to me as if it is working around a problem on the i2c >> master. I believe that a fix like this really belongs in the i2c >> master driver, it should be able to break the i2c transactions down >> into transactions that the i2c master can handle. >> >> I wouldn't want to merge this without a better explanation of why it >> is necessary in the tda18271 driver. It seems to be a band-aid to >> cover up a problem in the i2c master device driver code. > > Yes it is I2C provider limitation, but I think almost all I2C adapters have > some limit. I suggest to set param for each tuner and demod driver which > splits reads and writes to len adapter can handle. I did that for tda18218 > write. > > But there is one major point you don't see. It is not simple to add this > splitting limit to the provider. Provider does not have knowledge which is > meaning of bytes it transfers to the bus. Without knowledge it breaks > functionality surely in some point. There is commonly seen 1, 2 and 4 byte > register address and same for register values. Also some chips like to send > data as register-value pairs. Yes, I understand. We will likely merge Mauro's patch, I just want to test it on my own hardware first, and I'd like to verify the cx231xx i2c xfer limit issue that Mauro is reporting. I'll try to get back to this early next week, or hopefully over this weekend. Thanks for the input :-) Regards, Mike Krufky -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
