Messages in this thread | | | Subject | Re: [PATCH v5 1/2] gpio: add GPO driver for PCA9570 | From | Sungbo Eo <> | Date | Wed, 8 Jul 2020 23:30:36 +0900 |
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Thanks, it made me think about it deeper...
On 20. 7. 8. 오전 12:07, Andy Shevchenko wrote: > On Tue, Jul 7, 2020 at 5:03 PM Sungbo Eo <mans0n@gorani.run> wrote: >> On 20. 7. 6. 오후 9:00, Andy Shevchenko wrote: > > ... > >> But I don't really understand what mutex does here. The driver does not >> need consecutive commands, it only sends/receives only one byte at a >> time. And AFAIK each i2c_smbus function is already protected by a mutex. >> So what should be exactly inside the lock? Should we protect the output >> buffer as well? I'm not an expert on this so please enlighten me. > > There are questions, answering them will give you a solution: > - Since we have two functions doing i2c communications, can they > clash? If so, does the i2c framework guarantee the serialisation?
I think it does.
> - Since we have a shared resource (buf), can accessors clash? How do > we guarantee serialization? >
But the output buffer should be tied to the i2c operations. So I guess it requires a mutex here.
pca9570_get() does not access gpio->out so it does not need to be locked.
On the other hand, the whole pca9570_set() function should be protected, from reading gpio->out to rewriting to gpio->out. So pca9570_write() error check should be inside the lock as well. Am I right?
Thanks.
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